1. Field of the Invention
The present invention relates to photo-curing light systems for photosensitive compounds and more particularly to a photocuring light system having the ability to modulate light intensity.
2. Description of the Prior Art
There are numerous substances which are sensitive to light energy. One class of such substances are characterized by undergoing polymerization in response to applied light energy. This class of substances includes composites and adhesives that have found use in the dental arts with respect to tooth repair or the fabrication of dental prosthetics.
It is known that the time it takes to cure a photosensitive composite or adhesive is influenced by several factors. One is the type of composite or adhesive and the amount required for the application, a second is the intensity of the light energy delivered to the composite or adhesive in order to effectuate the cure of a composite or adhesive and a third is the time duration of exposure.
The typical light source in a high speed dental curing light is a Xenon arc lamp. The lamp""s spectral output extends from the ultraviolet (UV) to the infrared (IR). Filters are generally utilized in the optical path to reduce the deleterious heating effects from the infrared (IR). Further filtering is added to match the spectral response of the photo-initiators in the chemical compounds, (e.g. adhesives or composites) utilized in the dental procedures. The most common photo initiator is camphorguinone which has an absorption band in the visible spectrum with a peak of nominally 470 nm.
Typically, plasma arc curing lamps, such as a Xenon arc lamp have filtered spectral output ranges from 430 nm to 500 nm which matches the majority of the camphorquinone absorption band. In certain situations, other photo-initiators are utilized and in such instances with alternative photo-initiators, the absorption band shifts. For instance when the photo-initiator phenyl propanedione is utilized, it has a spectral peak at nominally 420 nm. Therefore the spectral range of the curing lamp must be expanded to cover this absorption band and this expansion of the absorption band may intrude into the ultraviolet spectrum. Expansion into a wider spectral output range results in additional photonic heating to the tooth structure adjacent to dental procedure. It is therefore desirable to be able to cure the desired chemical compounds (e.g. adhesives or composites) in a dental situation regardless of the photo-initiator utilized in the chemical compound while minimizing the increased heating. Applicant is able to accomplish this desired result by modulating the light output of the arc lamp.
An object of the present invention is to provide for a novel photo-curing system operable in a wider light spectrum.
A further object of the present invention is to provide for a novel photo-curing light system which can accommodate a plurality of photo-initiators having a variety of absorption bands.
A still further object of the present invention is to provide for a novel photo-curing light system which reduces additional heating to the tooth structure when operating in a wider spectral range.
Still further, an object of the present invention is to provide for a novel photo-curing light system by modulating the light intensity or output to reduce the heating factor.
A photo-curing light system in which modulation of the light intensity or output of the arc lamp is controlled via an analog control voltage to the control line output of the lamp power supply. The analog control voltage is digitally generated by a microprocessor and is converted to an analog signal with the use of a digital to analog converter integrated circuit feeding a constant current circuit using an operational amplifier integrated circuit. The control signal results in the lamp current being reduced from its maximum program value to a lower value. The proportion of the time that the lamp current is high divided by the total time period of the lamp current output is defined as the duty cycle. The amount of heat reduction is proportional to the duty cycle such that the lower the duty cycle, the lower the temperature rise in the tooth structure.